In natural teeth the periodontal ligament functions as a cushion between tooth and jawbone, absorbing impact force and uniformly transferring occlusal forces to surrounding bone. The distribution of the force depends on micro movement induced by the periodontal ligament. Due to lack of periodontal ligament, dental implant has to directly bond to bone, causing non-uniform stress distribution in bone which might lead to implant failure (Quirynen 1992). Because of the lack of micro movement of implants, most of the force distribution is concentrated at the crest of the ridge. Vertical forces at the bone interface are concentrated at the crestal regions, and lateral forces increase the magnitude of the crestal force distribution.
The most common failure mode of dental implant is loosening of implant induced by the atrophy of surrounding jawbone, which is generally caused by improper stress distribution on cervical bone under occlusion or mastication loading. As mentioned earlier, overloading and stress shielding have often been cited as the primary biomechanical factors leading to marginal bone loss around implants (Cehreli and Akca). Whether the bone loss after implantation is due to overloading or stress shielding still needs to be clarified. No matter which effect (overstressing or stress shielding) dominates the long-term performance of dental implant, it seems logical that excessive stress concentrations (possibly resulting from non-axial overloading) plays a critical role in early-stage marginal bone loss process.
Overloading has been identified as a primary factor behind dental implant failure. The peak bone stresses normally appear in the marginal bone. The anchorage strength is maximized if the implant is given a design that minimizes the peak bone stress caused by a standardized load. The design of the implant-abutment interface has a profound effect upon the stress state in the marginal bone when this reaches the level of this interface.